Electrical power line warning device for vehicles with extended booms



Oct. 28, 1952 A. H. ALBRECHT 2,615,969

ELECTRICAL POWER LINE WARNING DEVICE FOR VEHICLES WITH EXTENDED BOOMS Filed April 15, 1949 w R R w A m H w w M y Patented Oct. 28, 1952 ELECTRICAL POWER LINE WARNING DE- VHgEMFOR VEHICLES WITH EXTENDED BO S August H. Albrecht, La Habra, Califi; Esther V. Albrecht administratrix of said August H.

Albrecht, deceased Application April 15, 1949, SeriakNo. 87,654 T 1 Claim. (01. 177-311 The present invention relates to safety devices and, more particularly, to safety devices for vehicles having an extended boom, such as mobile crane units and the like.

panying drawing.

In the drawing, Fig. 1 is a schematic representation of a mobile crane unit approaching a power line with the side of the crane cut away to show the arrangement of the essential units of a machine which incorporates the present invention.

Fig. 2 is a wiring diagram of a circuit which may be used to operate the warning device in the cab of the crane.

In Fig. l, I have shown a mobile crane unit I of is applicable. Crane unit I is provided with the usual cab 2 which is rotatably mounted upon an endless-track propelling arrangement 3 by means of a bearing member 4. upon which the cab 2 may Inthe operation of vehicles having an extended 5 rotate with respect to the track 3. An engine boom, it is customary in moving from one loca- 5 and a transmission 6 are provided for both drivtion to another for an operator to drive the maing the crane unit and for operating the cable chine with the boom in a raised position so that drums l and 8 which respectively control the opa crane, or the like, will have a substantially eration of the hoisting hook pulley 9 and the shorter turning radius than would be possible 10 crane boom 10 by means of cables H and I2. with the boom lowered. However, this has been Levers I3 and I 4 are provided for the operator for hazardous in the past due to the frequent disoperating the usual clutches between transmisregard by the operator of overhead power lines sion 6 and the hoisting drums 1 and 8. which cross the path of the vehicle. Either due to As shown in Fig. l, crane l is generally moved the inability of the operator to see such lines or from one location to another with boom 10 in an the negligence of the operator, the boom is very elevated position, and in this position the end of likely to come in contact with the power line and the crane boom is liable to contact high tension may cause either failure of the power line or lines i5 which cross the path of the crane. It will create a very serious hazard for persons in the be apparent that the crane boom will be substanvicinity. Especially is the hazard severe for the tially at ground potential through the usual metal operator, who, in a number of instances, has been cab 2, bearing support 4, and track 3. Likewise, killed by electrocution when the boom has conit will be apparent that the seat I6 for the opertacted high tension lines. ator is in substantially the conducting path for It is, therefore, an object of this invention to any current passing from boom Hi to ground. provide a safety device to warn the operator of a Hence, the operator of the cab is in a very vulmobile crane unit and the like of the approach of nerable position if the boom runs into the power the boom of the machine to an electric power line line. In order to warn the operator of the crane so that the vehicle may be stopped and the boom of the approach of the boom to the power line, I moved before it contacts the power line. have provided a warning device capable of indi- It is a further object of this invention to proeating the approach of the boom at a distance vide a warning device that may be easily attached sufficient to permit the operator to stop the crane to a standard mobile unit having an extended and lower the boom. For this purpose, a signal boom for indicating the approach of the boom voltage pickup unit ll, which may be of either the to a power line at a sufficient distance so that the inductive type or of the Cgllacitative type, is 10- unit may be stopped and the boom lowered withcated upon an insulating redid-mounted adjaout danger of the boom shorting the power line cent the end of boom I0. While signal device I1 to ground through the machine. may be of either the inductive or capacitative A still further object of this invention is to type, in the preferred embodiment, a capacitative provide a warning device for a mobile crane havtype comprising a hollow metal sphere is used ing a sensitive pickup unit capable of indicating since it is possible with this type of device to the approach of the crane boom to a power line pick up a signal from the high tension lines l5 whether the line is loaded or not. whether or not a load current is being carried by Further objects and advantages of this inventhe power lines. Signal device I! is connected to tion will become apparent from the following deamplifier l9 which is located in the cab by means scription taken in conjunction with the accomof conductor 20. An automatic reeling device 2| is provided for conductor 20 to eliminate slack between the amplifier l9 and signalling device I! when boom 10 is raised or lowered. The usual battery 22 for starting and ignition of the engine 5 which is the prime mover for the crane, provides the operating potential source for amplifier l9, as well as the signalling devices 23 and meter 24, which are conveniently located in cab 2 to warn the operator of the approach of the end of boom [0 to the lines l5.

Referring now to Fig. 2, signal pickup unit I! is connected to amplifier l9 through line as described hereinbefore. However, a switch is normally provided between line 20 and the amplifier for disconnecting the signal source from the amplifier. If so desired, switch 25 may be operated as a limit switch by the location of boom H) in respect to cab 2 of the crane unit so that when the boom is lowered the signal may be automatically interrupted. The signal voltage from pickup unit I! is then applied to the amplifier through line 25 and resistor 21 which has its other terminal connected to ground. Resistor 21 serves as a leak resistance and is one of the controlling factors determining the amount of potential available from signal unit I! that may be applied to the amplifier. A potentiometer 28 is connected in parallel across resistor 21 and a movable contact 29 for potentiometer 28 is provided for supplying an operating potential to the control grid 30 of the detector tube 3| by means of line 32. As shown, tube 3| is of the pentode type with a suppressor grid 33 directly connected to cathode 34 of the tube and with a grid biasing resistor 35 directly connected between the cathode terminal and ground. Plate 36 and screen grid 31 are connected to a plate voltage supply (not shown) through resistors 38 and 39, respectively. A screen by-pass condenser 40 is connected between the screen grid and ground. The output of tube 3| is coupled to a pair of triode tubes 4| and 42 which serve as phase inverters for the subsequent push-pull amplifier stage provided by tubes 54 and 55. In a manner well known in the art, grid 43 of triode 4| is connected to the plate of pentode tube 3| through coupling condenser 44 and a load resistor 44'. However, grid 45 of triode 42 is connected to a point intermediate resistors 45 and 56 which are connected to serve as both a load resistor for tube 4| and as a voltage divider circuit. By this arrangement tube 42 is adapted to operate in phase with pentode 3| while tube 4| is substantially 180 out of phase with pentode 3|. It will be understood by those skilled in the art that resistors 45 and 56 may be so proportioned that the output voltage from tubes 4| and 42 may be equal with the phase inverted. Cathodes 41 and 48 of triodes 4| and 42 are directly connected to one end of a resistor 49 which in turn is connected to ground and serves as a common grid biasing resistor for both tube 4| and 42. Plates 50 and 5| of thetriodes are respectively connected to a plate potential source through resistors 52 and 53.

As stated hereinbefore, a push-pull stage of amplification is provided by a pair of screen grid tubes 54 and 55. The control grid of tube 54 is coupled to the output of tube 4| through coupling condenser 5! and resistors 46 and 55, while the control grid of tube 55 is connected to the output of tube 42 through coupling condenser 58 and load resistance 59. Cathodes 60 and El of the screen grid tubes are directly connected to a common grid biasing resistor 62. Plates 53 and 84, respectively, of tubes 54 and 55 are connected across the ends of a primary coil of output transformer 55. In order to provide the required operating potential for the screen grids and the plates of tubes 54 and 55, the screen grids are connected together and a source of positive potential is directly applied to the screen grids and likewise connected to the plates 63 and 64 through center tap 6! on primary coil 55.

In order to provide the desired operating po- 4 tential for warning devices 23 and meter 24, secondary coil 68 of transformer 66 is connected to a rectifier, such as double-diode tube 69. As shown, plates 10 of rectifier tube 69 are con- 5 nected to one end of secondary coil 68 while the opposite end of the coil is directly connected to round. Cathodes H of rectifier 69 are connected to ground through ammeter 24 and through both the coil of relay 14 and resistor '12 10 which are connected in parallel. Preferably, but

not necessarily, a by-pass condenser 13 is provided between cathodes H and ground, and likewise, a resistor 15 is provided across a portion of secondary 68 of transformer 65.

With meter 24 connected in the output circuit of rectifier 69, means are provided for continuously indicating the amount of current flowing between pickup unit I! and resistor 21, and by properly selecting resistor 12 in relation to the 20 coil of relay I4, a predetermined voltage developed across rectifier tube 69 will actuate armature 15 of relay 14. 'As shown, armature 15 is adapted to close contacts 11 and 18, which are respectively connected between the power battery 22 and the coil 19 of relay 80. While any number of warning devices 23 may be connected to the battery 22, it has been found desirable to connect a lamp 23 directly to the battery 22 through contacts 11 and 18 and armature 16 of 30 relay 14, so that a signal will be present at all times when the current in the output circuit of the amplifier is sufiicient to indicate the presence of the crane boom adjacent to the power line. As stated before, coil 19 of relay B0 is in parallel with the lamp 23 and hence the coil is energized at the same time that the lamp is lighted. Armature 82 of relay is designed to close a set of contacts 83 and 84 to place a second warning device, such as bell 23", directly across 40 the battery. However, relay 85 is of the time delay type and may be arranged to be de-energized after a specified period of time. In this way, both lamp 23 and bell 23" will be energized as soon as the boom approaches the power a line, but after a predetermined time bell 23" may be de-energized, leaving only the lamp 23' as a warning element.

In operation, the mobile crane unit I is generally driven from one location to another with 50 boom 0 in an elevated position and in this posi tion the boom is very likely to come in contact with overhead high tension lines l5. However, with pickup unit installed above the end of the crane boom, and with limit switch 25 in a 55 closed position, the pickup unit I1 is adapted to pick up a signal voltage from the power line l5 upon the electrostatic principle. Under these conditions, unit ll acts as one plate of a condenser with the wires 5 acting as the opposed 60 plate of the condenser and the intervening space between unit I! and wires I5 acting as the dielectric of the condenser. In this manner a voltage is impressed upon pickup unit H and this in turn is applied to the amplifier l9 through resistors 27 and 2B. The movable contact 29 is provided on resistor 28 so that sensitivity of the amplifier may be adjusted and the desired portion of the signal voltage generated in-unit I! applied to the amplifier. In the amplifier the current flow in .tube 3| is controlled by grid 30 and the output of ptube 3| is applied to tubes 4| and 42, which, as stated hereinbefore, are adapted to serve as a phase inverter circuit to produce equal voltages which are substantially out of phase with each other, with tube 4| being out of phase with tube 3| while tube 42 is in phase with tube 3|. An amplification stage is then provided for the signal voltage by tubes 54 and 55, which are coupled to the output circuits of tubes 4| and 42. The output of this stage of amplification is then applied to a coupling transformer, which in turn is connected to rectifier tube 69. When the strength of the signal voltage is sufiiciently high, the current flow through tube 69 may be adjusted to actuate the coil of relay 14. When the coil of relay 14 has been energized, the contacts 11 and 18 are closed to connect the warning light 23 and bell 23" to the power source, battery 22. When the operator of the crane is thus warned of the approach of the end of boom [0 to the power line, he may stop the crane and properly adjust the boom to a point where it will not contact the power line.

By the foregoing arrangement, a very effective warning device is provided for the operator of a vehicle having an extended boom so that the life of the operator, as well as other workmen, will not be endangered by the boom contacting a high tension line and shorting the line to ground through the machine.

It will be apparent to those skilled in the art that the electrostatic unit I! may be replaced by an electromagnetic type of pickup wherein a voltage is generated in a coil by the magnetic lines of force generated in the air space between the coil and the high tension lines. It will also be obvious that numerous changes may be made in the electronic amplifier without departing from the scope of the invention, and that the only requirement of the amplifier is that it convert the signal voltage or current to an operating potential for the warning devices.

Among the modifications that may be made in this system without departing from the scope of the invention is the possibility of interconnecting the ignition system for the internal combustion engine driving the crane with the relay system for the warning devices. Thus, when the signal voltage is sufiicient to actuate relay 14, the engine may be stopped. If a gas engine is used in propelling the crane, the relay could operate to open the ignition system or ground the magnetos, or, if a diesel engine is used, the relay may be used to close the fuel line.

While the warning device is shown in the preferred embodiment to be incorporated in a' mo- -.bile crane unit, it will be appreciated that this system can be applied to any equipment having an extended boom where there is likelihood of .contacting an overhead power line while moving the machine from one location to another.

Other variations and modifications of the invention may be made without departing from the scope of the invention, and I, therefore, intend to limit the invention only within the scope of the appended claim I claim:

In combination, a vehicle having an extending boom, said boom being continuously in electric contact through said vehicle with the earth so that it is at ground potential, a capacitor pickup unit mounted adjacent the end of said boom and insulated therefrom, an amplifier mounted on said vehicle and connected directly to said pickup unit for amplifying the signal impressed upon said unit, means for continuously energizing said amplifier when either said vehicle or said boom is in motion, and warning means connected to the output of said amplifier for indicating the approach of said boom to an overhead electric 1 power line whereby the operator may stop said vehicle or adjust said boom before said boom contacts said overhead power line.

AUGUST H. ALBRECHT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,696,230- Gilbert Dec. 25, 1928 1,857,172. Wagner May 10, 1932 v2,l31,291 Maust Sept. 27, 1938 2,142,304 Cummings Jan. 3, 1939 2,343,981 Lindsay Mar. 14, 1944 2,428,360 Dingley Oct. '7, 1947 FOREIGN PATENTS Number Country Date 243,628 Switzerland Jan. 16, 1947 l ver 

